Director

Director can be used by Dovecot's IMAP/POP3/LMTP proxy to keep a temporary user -> mail server mapping. As long as user has simultaneous connections, the user is always redirected to the same server. Each proxy server is running its own director process, and the directors are communicating the state to each others. Directors are mainly useful for setups where all of the mail storage is seen by all servers, such as with NFS or a cluster filesystem.

First test non-director proxying

The director is simply a small add-on for Dovecot proxy. Before configuring director, you should test that a simple proxying setup with static destination server works. See the Proxy page for more information about how to configure it. If you have a simple setup, you can test this easily using a static passdb:

passdb {
driver = static
args = proxy=y host=10.2.0.20 nopassword=y
}

Once finished testing, remember to remove the "host" field.

Servers

You need one or more servers assigned for Dovecot proxies. The same servers could also act as backends handling the mails, but you need to run two separate Dovecot configurations in different ports. This may get a bit confusing, so it's not recommended (although v2.1 makes it easier with instance_name setting).

The directors are going to connect to each others in a ring. For example if you have servers called A, B and C, director will create connections A->B, B->C and C->A.

Director configuration

In example configuration you can configure director from conf.d/10-director.conf.

The port 9090 will be used for listening and connecting to other directors. You're free to use any port number you want.

Configuring list of director servers

List all of your directors in director_servers setting separated by spaces. You can use:

IP addresses

hostnames

hostnames that expand to multiple IPs (e.g. you could have a "directors-all" DNS entry that expands to all directors' IPs)

You can also add :port after the IP/host. The default port is the same as what director service's inet_listener is using (the port 9090 above).

Note that the same director must not be listed multiple times with different IPs. This especially means that a hostname can't expand to both IPv4 and IPv6 address. Otherwise Dovecot becomes confused about what directors actually exist. This also means that a single director ring must use either IPv4 or IPv6 addresses, but not both at the same time.

For example if you have 3 directors, you could set:

director_servers = 10.1.0.2 10.1.0.3 10.1.0.4

Configuring list of mail servers

List all of your backend mail servers in director_mail_servers setting separated by spaces. You can use:

IP addresses

IP ranges (e.g. 10.2.0.10-10.2.0.30)

hostnames

hostnames that expand to multiple IPs

For example if you had 20 mail servers with consecutive IPs:

director_mail_servers = 10.2.0.11-10.2.0.30

Enabling director

Enable director for the wanted login services by telling them to connect to director socket instead of the default login socket:

By default LMTP proxy connects to the same port in backend as what was used for the incoming connection.

Other settings

Directors redirect a user to the same server always the user has active connections. The redirection is also done for a while after the last connection already disconnected. This is mainly to avoid trouble with NFS caches that haven't yet expired. You can configure this setting from:

director_user_expire = 15 min

doveadm director kick and doveadm director move need to be able to connect to the ipc socket. Make sure the director process can do it:

service ipc {
unix_listener ipc {
user = dovecot
}
}

Passdb configuration

Director works by adding a "host" extra field to the auth reply, which contains the temporary destination mail server. This "host" field isn't added if the passdb lookup already returns "host". This allows configuring some users to be always proxied to a specific server.

If the backend servers verify password, you can use static passdb for director:

passdb {
driver = static
args = proxy=y nopassword=y
}

Note that while this is the simplest director configuration, users will be assigned to a backend before they have been authenticated. A director configured this way can be attacked by sending it a large number of unknown users. To prevent this, the director should be configured to authenticate the user and might make use of a master password to log into the backend servers.

Doveadm server

Use these settings for both director and backends:

service doveadm {
inet_listener {
# any port you want to use for this:
port = 24245
}
}
local 10.10.10.0/24 {
# password to use for client authentication
doveadm_password = secret
# allow client to only use specified list of commands (default is all):
#doveadm_allowed_commands =
}

Forcefully moving users to a different backend

This is useful if you need to do maintenance on one of the backend servers and want (active) clients to move to a different backend:

Disable any watchdog system that will undo changes you make to backend server weights, such as poolmon.

Not needed if the watchdog is new enough to use HOST-UP/HOST-DOWN commands rather than change weights.

Set the weight of the backend server to be worked on to 0: doveadm director add <backend server ip> 0

Flush current assignments to disable new connections to this backend: doveadm director flush <backend server ip>

This will also kick the existing connections to the backend in v2.2.19+.

Most IMAP clients will silently just reconnect to the (new backend) server after being kicked (at least Apple Mail 6.0 and Thunderbird 14.0).

For moving specific users to other servers (e.g. because there are too many "heavy users" assigned to the same backend), you can use doveadm director move command in v2.0.14+. This requires the ipc permissions to be configured correctly (see above).

Tags

(Requires v2.2.16+)

WARNING: This feature isn't working perfectly in v2.2.26.1 and older. If two users with different tags have the same 32bit hash, they may end up going to the wrong tag's backend.

With tags you can use a single director ring to serve multiple backend clusters. Each backend cluster is assigned a tag name, which can be anything you want. By default everything has an empty tag. A passdb lookup can return "director_tag" field containing the wanted tag name. If there aren't any backend servers with the wanted tag, it's treated the same as if there aren't any backend servers available (= wait for 30 secs for a backend and then return temporary failure).

Tags can be added to configuration by adding @tag suffix to IPs/hosts. For example:

director_mail_servers = 10.0.0.100-10.0.0.110@name1 10.0.0.120@name2

"doveadm director add" can also add tags either with @tag suffix or with -t parameter. "doveadm director status user@domain" requires giving the user's correct tag with -t parameter or the results won't be correct (empty tag's results are shown). Tags can't currently be changed for an existing host without removing it first.

Director and Backend in same server (broken)

NOTE: This feature never actually worked. It would require further development to fix (director would need to add "proxy" field to extra fields and notify auth that the auth_request can be freed).

Have the passdb lookup return director_proxy_maybe=y. LMTP however doesn't currently support mixing recipients to both being proxied and store locally.

Flush socket

(Requires v2.2.26+)

This allows calling a script for each user (hash) that is moved between backends. This is triggered by "doveadm director move" and "doveadm director flush" commands. What happens is:

User's connections are kicked from the director cluster

Flush socket is called and waited on.

User logins are delayed until the flush socket is finished, or the user move times out after 30 seconds (hardcoded).

Only the director that initiated the doveadm command will call the flush socket.

director_user_kick_delay is ignored by the initiating director, but used by the other directors.